Improving Cyclone, Earthquake and Tsunami Resistance of Houses

Transcription

1 Improving Cyclone, Earthquake and Tsunami Resistance of Houses Photo: Cyclone Damage on Aitutaki in the Cook Islands Courtesy of D Kaunitz (Emergency Architects Australia)

2 Improving Cyclone, Earthquake and Tsunami Resistance of Houses in the Asia / Pacific Region Two levels of improvement are applicable. 1. Anchor points with temporary tie ropes. The anchor points are permanent and may be constructed cheaply. The tie ropes may be positioned and tightened at the commencement of the cyclone season (if not already in place). This is a cheap quick fix, but is reasonably unattractive and provides only modest improvement. 2. Additional roof fixings and cyclone washers, roof framing anchors, timber diagonal bracing, steel diagonal bracing and/or sheet bracing. These are permanent structural features that should be installed as part of the construction of new buildings, but are often missing. They may be retro-fitted to existing buildings. Both levels of improvement should be undertaken commencing with Anchor points with temporary tie ropes in an initial program, and progressing to the more permanent features when there is sufficient funding.

3 External Anchor Points with Temporary Tie Ropes

4 Anchor Points with Temporary Tie Ropes The first step in improving cyclone resistance is to construct strong anchor points, to which the roof tie ropes can be fixed. The spacing of anchor points should not exceed 3.0 metres. There are two types on roof ties: 1. Roof ties that prevent roofing sheets from being blown off the house once it has become loosened by the wind. These generally run end-to-end along a gable roofed house. These are the most common form of roof tie. 2. Roof ties that anchor the roof framing to the walls and run across a gable roof. 1. Ties to secure roof sheets 2. Ties to secure roof to walls Anchor points on both ends under the edge of the building Anchor points on both sides under the edge of the building

5 Anchor Points and Tie Ropes to Restrain Roof Sheeting Although tie ropes that run from end-to-end will generally not be tight enough to prevent the sheeting for tearing loose from the roofing battens, they will prevent the sheeting from then being blown off the house. In gable roof houses, the anchors for these tie ropes should be positioned opposite each other on both ends of the house, so that the tie ropes run across all roof sheets. The ideal position for anchor points is under the edge of the building. This is because the weight of the building can be used to prevent the anchor points from being pulled out by strong wind. The spacing of anchor points should not exceed 3.0 metres. Anchor points on both ends under the edge of the building

6 Anchor Points and Tie Ropes to Secure the Roof to the Walls Anchor points for roof ties (running across a gable-roofed house) that secure the roof framing to the walls should be positioned opposite each other on both sides of the house. The ideal position for anchor points is under the edge of the building. This is because the weight of the building can be used to prevent the anchor points from being pulled out by strong wind. Ties that pass over the roof sheeting will anchor some of the sheets, the battens and roof framing. They are more likely to be pulled tight than ties that run from end to end, but cannot anchor all of the roof sheets. Ties that pass over the battens but under the roof sheeting will anchor the battens and roof framing, but will not secure the roof sheeting. Anchor points on both sides under the edge of the building

7 Remote Anchor Points If it is impractical to place the anchors under the edge of the building or to fix the tie ropes the bottom of the posts, special anchor points may be constructed beside the building. They must have sufficient weight or be buried deep to provide sufficient resistance to uplift. Remote anchor points on both sides of the building. Must be buried deep. Do not tie the building to trees or other small structures, because they may be blown away by high wind.

8 Permanent Remote Concrete Anchor Points Concrete anchor points provide durable permanent remote anchorage. Capacity in the range of 120 kg to over 2 tonnes, depending on the side and depth of concrete, and total depth from the surface to the underside of the concrete. Burying the anchor point significantly increases the skin friction between the soil and concrete. Recommended sizes (depending on application) are shown in large black type. Uplift Capacity of Square Concrete Anchor Blocks in Sand Length of side mm Depth of concrete mm Depth from surface to underside of concrete mm ,000 1,000 1,000 Volume of concrete m Factored uplift capacity kn Factored uplift capacity tonnes Depth from surface to underside of concrete Depth of concrete N12 reinforcement anchor 12 mm diameter 500 MPa reinforcing steel x 2,000 mm long, with standard hooks plus 400 mm embedment length on each of two legs, compacted 20 MPa concrete. Compacted soil above concrete (if applicable) N20 concrete (20 MPa) with steel anchor point set in position Side

9 1.5 tonne Capacity Permanent Remote Concrete Anchor Points 1. Excavate 450 x 450 x 1,000 deep hole. 2. Bend N12 reinforcement anchor. 3. Prepare a mold out of a 100 dia x 700 mm pipe, split down one side and hold together by two rings. 1,000 mm depth from surface to underside of concrete 450 mm depth of concrete 4. Place the anchor and install N20 concrete. Install the mold around the anchor. N12 reinforcement anchor 12 mm diameter 500 MPa reinforcing steel x 2,000 mm long, with standard hooks plus 400 mm embedment length on each of two legs, compacted 20 MPa concrete. Compacted soil above concrete (if applicable) N20 concrete (20 MPa) with steel anchor point set in position 5. Remove the mold. 6. Expose the anchor Backfill and compact soil leaving anchor point exposed.

10 Epoxied Eye-bolt Slab Edge Anchor Point 1. Ensure that the concrete slab is of sufficient strength (at least 10 MPa) and thickness (at least 150 mm thick). Otherwise the anchor will rupture the concrete and pull out under wind load. 2. Drill holes in the concrete of the specified diameter, depth, edge distance and spacing. 3. Ensure the hole is clean. 4. Insert and fix the anchor in two-part epoxy as per the manufacturer s instructions. 5. Fix tie ropes. Eye-bolts epoxied in concrete slab edge Eye-bolt size Eye-bolt effective depth Diameter of hole drilled in concrete In-situ concrete strength Minimum edge distance (bolt centre to edge) Factored shear capacity of anchor M mm 14 mm 10 MPa 75 mm 5.1 kn 0.5 tonnes Eye-bolt specification: M MPa bent steel eye-bolt Rope Specification: Polypropylene twisted 3 strand 12 mm dia rope (R00QE)

11 Chemset Slab Edge Anchor Point 1. Ensure that the concrete slab is of sufficient strength (at least 10 MPa) and thickness (at least 150 mm thick). Otherwise the anchor will rupture the concrete and pull out under wind load. 2. Drill holes in the concrete of the specified diameter, depth, edge distance and spacing. 3. Ensure the hole is clean. 4. Insert and fix the Chemset anchor in accordance with the manufacturer s instructions. 5. Bolt the connection bracket to the anchor if required and fix tie ropes. Chemset in concrete slab edge Chemset size Chemset effective depth Diameter of hole drilled in concrete In-situ concrete strength Minimum edge distance Factored shear capacity of anchor M mm 14 mm 10 MPa 75 mm 5.1 kn 0.5 tonnes Chemset specification: M12 x 110 depth Rope Specification: Polypropylene twisted 3 strand 12 mm dia rope (R00QE)

12 House Foundation Anchor Point 1. Excavate holes in the foundation under the edge of the house footings. 2. Bend 10 mm reinforcing bars to provide two legs, each with standard hooks, as shown. Hold the bars in position by timber supports. 3. Place and compact 20 MPa concrete (1 part cement : 2 parts sand : 4 parts gravel) in the holes. 4. Remove the support timbers. R10 reinforcement anchor Standard hook plus 400 mm embedment length on each leg Number of legs 2 Factored capacity of anchor ϕ N u anchor 35 kn 3.6 tonnes N12 reinforcement anchor 12 mm diameter 500 MPa reinforcing steel x 2,000 mm long, with standard hooks plus 400 mm embedment length on each of two legs, compacted 20 MPa concrete.

13 Temporary Edge Anchor Point If permanent materials such as steel and concrete are not available, temporary edge anchor points may be constructed from timber and rope. These may be liable to termite attack or deterioration, and must be inspected regularly and renewed if necessary. 1. Excavate under the edge of the building. 2. Fix a rope loop to the diagonal strut, as near as practical to the top. 3. Position the top end of the diagonal timber strut as far as practical under the footing, and hammer the bottom end into place. 4. Pull the rope loop free, backfill and compact the soil. ` 150 x 150 x 1,200 timber strut with rope anchor point (6 strands of polypropylene twisted 3 strand 8 mm dia rope) tied to the top end. Strut to be wedged into position diagonally at 45 o. Backfill with compacted soil. Capacity in compacted sand: ϕ N = 25 kn

14 3 2 1 Temporary Remote Anchor Points If permanent materials such as steel and concrete are not available, temporary remote anchor points may be constructed from timber pegs. These may be liable to termite attack or deterioration, and must be inspected regularly and renewed if necessary. 1. Hammer three large timber pegs deep into the ground, and tie them together. 2. Behind this, hammer two large timber pegs deep into the ground, and tie them together. 3. Behind this, hammer one large timber peg deep into the ground. 4. Tightly tie the bottom of the rear peg to the top of the middle two pegs, and the bottom of the middle two peg to the top of the front three pegs. 5. Compact all of the ground surrounding the anchorage. 6. The anchorage is now ready for the tie rope to be fixed to the bottom of the front three pegs. 6 pegs 150 x 150 x 1,200 Tied tightly top to bottom with 6 strands of Polypropylene twisted 3 strand 8 mm dia rope Capacity in compacted sand: ϕ N = 25 kn

15 Connection Bracket for Slab Edge Anchor Point Anchors commonly (but not always) consist of an eye-bolt set in the slab edge. Where the anchor is a stud with nut, this connection bracket may be used tho provide a hole through which a tie can pass. 1. Bolt the connection bracket to the anchor. 2. Ensure that there are no sharp edges in the holes that could tear any rope ties. Use packing if appropriate f sy = 250 MPa x 6 Plate x 160 long 2 Holes 20 mm diameter Tensile Capacity: 54 kn (5.5 Tonnes)

16 Additional Roof Fixings and Cyclone Washers, Roof Framing Anchors, Timber Diagonal Bracing, Steel Diagonal Bracing and/or Sheet Bracing

17 Additional Roof Fixings and Cyclone Washers Cyclonic wind can suck the roof sheeting off the roof framing if there is an insufficient number of appropriate roofing screws, or if the roofing screws have been installed without cyclone washers. Insert additional roofing screws with cyclone washers through ribs that do not already have screws. Roof sheets shall be fixed through the high point of the ribs using long screws, not valley fixed. Roof sheets shall be laid in continuous lengths where practical, with the upper end turned up using the correct tool. In very high wind areas, turn the sheets down into the eaves gutter at the lower end. AS 4055 Wind Classification N1 N2 N3 N4 C1 N5 C2 N6 C3 C4 Maximum end span without cyclone washers Not suitable Not suitable 950 Maximum end span with cyclone washers 1, Not suitable Not suitable Number of ribs to be fixed Every second rib Every rib Every rib Not suitable Not suitable Maximum internal span without cyclone washers Not suitable Not suitable 1,200 Maximum internal span with cyclone washers 1, Not suitable Not suitable Number of ribs to be fixed Every third rib Every rib Every rib Not suitable Not suitable Notes: 1. In some cirmstances, engineering analysis of test results may give improved spans. 2. Refer to roofing manufacturer's technical manuals for specification of fixing screws, details and material compatibility. 3. References include: Lysaghts "Cyclonic Area Design Manual". Suitable Spans and Fixing Arrangemetns of Corrugated Steel Sheeting (0.42 mm BMT)

18 Roof Framing Fixings Cyclonic wind can suck the roof framing off the timber wall framing if there is an insufficient number of appropriate ties, or if the ties are not correctly fixed to the wall framing. Capacity 13.0 kn Based on AS Table 9.17 Nominal nailing 30 x 0.8 mm galvanised steel strap looped over the chord of the roof frame and under the top plate, and each end fixed by 5-30 x 2.8 mm φ galvanised flat-head nail.

19 Roof Anchors for Reinforced Concrete Masonry Bond Beams Cyclonic wind can suck the roof framing off concrete blockwork buildings if the roof anchorages are inadequate. In reinforced hollow concrete block walls, use steel cleats to tie the roof framing to horizontal steel reinforcement in the reinforced concrete masonry bond beams. Use the Bond Beam Fishtail Anchorage Cleat for bond beams consisting of two courses and the Bond Beam Single Anchorage Cleat for bond beams consisting of one course. Anchorage tests at James Cook University

20 Fishtail Roof Anchors for Reinforced Concrete Masonry Bond Beams Capacity 190 mm reinforced masonry 30.7 kn 140 mm reinforced masonry 23.3 kn Based on AS Table M16 bolted connection in accordance with AS f sy = 250 MPa x 6 Plate x 460 long Hot dip galvanised 50 x 6 Plate x 460 long Hot dip galvanised N12 or N16 horizontal steel reinforcement grouted within the bond beam, tied by N12 or N16 reinforcing bars to starter bars in concrete slab-on-ground Nominal 390 x 190 x 190 mm reinforced hollow concrete masonry Form a fish tail by bending each side of the cleat though 30 o.

21 Single Roof Anchors for Reinforced Concrete Masonry Bond Beams Capacity 190 mm reinforced masonry 13.1 kn 140 mm reinforced masonry 11.3 kn Based on AS Table M16 bolted connection in accordance with AS f sy = 250 MPa x 6 Plate x 260 long Hot dip galvanised 2 Holes 20 mm diameter 50 x 6 Plate x 260 long Hot dip galvanised N12 or N16 horizontal steel reinforcement grouted within the bond beam, tied by N12 or N16 reinforcing bars to starter bars in concrete slab-on-ground 30 Nominal 390 x 190 x 190 mm reinforced hollow concrete masonry

22 Lateral Bracing Failure to provide adequate cross bracing will make a building liable to collapse due to racking action caused by wind, earthquake or tsunami. This may be prevented by installing: Wall bracing, and Subfloor bracing (in elevated buildings).

23 Wall Bracing Two Diagonally Opposed Timber or Metal Braces Capacity 0.8 kn/m length Based on AS Table 8.18 (a) 45 x 19 mm or 70 x 19 mm hardwood timber braces fixed to each stud and plate by 1-50 x 2.8 mm φ galvanised flat head nail OR 18 x 16 x 1.2 mm galvanised steel angle brace fixed to each stud by 1-30 x 2.8 mm φ galvanised flat-head nail and nailed to the top and bottom plates by 2-30 x 2.8 mm φ galvanised flat-head nails. Angle of braces from horizontal between 30 o and 60 o. Fix bottom plate to floor frame or concrete slab with nominal fixings 1,800 to 2,700mm 1,800 to 2,700mm

24 Wall Bracing Pairs of Tensioned Metal Straps Capacity 1.5 kn/m length Based on AS Table 8.18 (b) 45 x 19 mm or 70 x 19 mm hardwood timber braces fixed to each stud and plate by 1-50 x 2.8 mm φ galvanised flat head nail OR 18 x 16 x 1.2 mm galvanised steel angle brace fixed to each stud by 1-30 x 2.8 mm φ galvanised flat-head nail and nailed to the top and bottom plates by 2-30 x 2.8 mm φ galvanised flat-head nails. Angle of braces from horizontal between 30 o and 60 o. Fix bottom plate to floor frame or concrete slab with nominal fixings 1,800 to 2,700mm

25 Wall Bracing Timber or Metal Angle Braces Capacity 1.5 kn/m length Based on AS Table 8.18 (c) Detail 1 Detail 1 Detail 1 Four sets of ties, each 30 x 0.8 mm galvanised steel strap looped over the top or bottom plates and fixed to the stud on both sides by 3-30 x 2.8 mm φ galvanised flat head nails 75 x 15 mm F8 timber brace fixed to each stud and plate by 2-50 x 2.8 mm φ galvanised flat head nails OR 20 x 18 x 1.2 mm galvanised steel angle brace fixed to each stud by 2-30 x 2.8 mm φ galvanised flat-head nails Depth of notch or saw cut in studs shall not exceed 20 mm Drill if necessary to avoid end splits. Angle of braces from horizontal between 30 o and 60 o. Detail 1 Fix bottom plate to floor frame or concrete slab with nominal fixings Detail 1 1,800 to 2,700mm

26 Wall Bracing Tensioned Metal Straps with Stud Straps Capacity 3.0 kn/m length Based on AS Table 8.18 (d) Detail 1 Detail 1 Detail 1 Four sets of ties, each 30 x 0.8 mm galvanised steel strap looped over the top or bottom plates and fixed to the stud on both sides by 4-30 x 2.8 mm φ galvanised flat head nails 30 x 0.8 mm galvanised steel strap fixed to each stud by 1-30 x 2.8 mm φ galvanised flat-head nail and nailed to the top and bottom plates by 2-30 x 2.8 mm φ galvanised flathead nails. Angle of braces from horizontal between 30 o and 60 o. Detail 1 Fix bottom plate to floor frame or concrete slab with nominal fixings Detail 1 1,800 to 2,700mm

27 Wall Bracing Plywood Sheeting Without Additional Connections Capacity 3.4 kn/m length Based on AS Table 8.18 (g) Plywood sheets fixed: Around perimeter to top plate, bottom plate and end studs at 150 mm centres by 30 x 2.8 mm φ galvanised flat head nails; and To internal studs (and noggings where required) at 300 mm centres by 30 x 2.8 mm φ galvanised flat head nails. Sheets may be butt jointed horizontally, provided they are fixed horizontally at the edges to noggings. Provide an additional row of nogging at half height of the wall, if required. Minimum Plywood Thickness Stud Spacing 450 mm 600 mm 450 mm 600 mm Stress No nogging (except at Grade horizontal butt joints) One row of nogging F8 7 mm 9 mm 7 mm 7 mm F mm 7 mm 4.5 mm 4.5 mm F14 4 mm 6 mm 4 mm 4 mm F27 3 mm 4.5 mm 3 mm 3 mm Sheathed panels shall be fixed to the sub-floor. Fix the bottom plate to floor frame or concrete slab with nominal fixings.

28 Sub-floor Tension Bracing Capacity 15 kn Based on AS Table 8.9 Columns, of dimensions not less than: 90 x 90 mm F11 (or stronger) hardwood 90 x 90 mm N20 (or stronger) concrete with 1 N12 reinforcing bar Alternative Detail: Where practical, fix diagonal braces at the top directly to the bearers, to provide a more direct load path to the ground 3,000 maximum 150 minimum Bearers fixed to columns with 1-M12 bolt or 2-M10 bolts 190 x 190 mm 15 MPa reinforced concrete masonry with 1 N12 reinforcing bar 90 OD x 3 mm CHS galvanised steel hollow section Two diagonal braces, 90 x 45 mm F11 (or stronger) hardwood, fixed to columns at the bottom and to the bearer (preferred) or column at the top by 1-M16 bolt (or stronger). Angle of braces from horizontal between 30 o and 60 o. 130 minimum 2,000 minimum - 3,600 maximum

29 Sub-floor Compression Bracing Capacity 15 kn (Nominal) 200 minimum Bearers fixed to columns with 1-M12 bolt or 2-M10 bolts Depth of notch minimum 3,000 maximum Columns, of dimensions not less than: 200 x 200 mm or 250 mm diameter F11 (or stronger) hardwood, or 150 x 150 mm or 200 mm diameter N20 (or stronger) concrete with 1 N12 reinforcing bar Two diagonal braces in opposing directions in two bays on each side of building, at least 90 x 90 mm or 150 mm diameter F11 (or stronger) hardwood, notched into the columns to a depth of 50 mm and fixed at the top and bottom by at least x 3.15 mm φ galvanised flat head nails (or stronger). 2,000 minimum - 3,600 maximum Angle of braces from horizontal between 30 o and 60 o.

30 Builder: Site: Activity: External Anchor Points and Tie Ropes Construction Checklist Item or Product Inspection Required Accept Criteria Hold Witness Installation procedures Visual inspection Latest issue on site Hold Location of anchor points Visual inspection As per procedures Hold Condition of concrete slab Hit with hammer No shattering of cracking Condition of adjacent rock Hit with hammer No shattering of cracking Condition of soil Dig 500 mm test hole Firm soil with no rock or tree roots Select appropriate anchor type Check procedures and As per procedures required capacity Install the anchors as per the relevant Visual inspection Installed as per procedures procedures Hold Hold Hold Hold Witness Date Inspector Comment Proof load using the Load Tester Install tie ropes and partially tighten tie ropes Label, remove and store tie ropes Apply proof load of half the nominated capacity or 0.5 tonne (whichever is less) to 5% of installed anchors Must support the calculated proof load without loss of capacity Witness Visual inspection As per procedures Witness Inspect and count stored tie ropes. Check register All ropes must be marked, stored and registered Witness

31 Builder: Site: Activity: Roof Fixing and Roof Anchors Construction Checklist Item or Product Inspection Required Accept Criteria Hold Witness Installation procedures Visual inspection Latest issue on site Hold Location and condition of existing roof fixings and internal anchors Select appropriate types of roof fixings and internal roof anchors Install the appropriate roof fixings and internal roof anchors as per the relevant procedures Visual inspection and assessment of installed capacities Check procedures and required capacity Visual inspection Provide required design capacity As per procedures Installed as per procedures Hold Hold Witness Date Inspector Comment

32 Builder: Site: Activity: Wall and Sub-floor Bracing Construction Checklist Item or Product Inspection Required Accept Criteria Hold Witness Installation procedures Visual inspection Latest issue on site Hold Location and condition of wall and subfloor bracing Select appropriate types of wall and sub-floor bracing Install the appropriate wall and sub-floor bracing as per the relevant procedures Visual inspection and assessment of installed capacities Check procedures and required capacity Visual inspection Provide required design capacity As per procedures Installed as per procedures Hold Hold Witness Date Inspector Comment

33 Engineering Calculations The following engineering data is provided for general information only. The design of the structure must be carried out be a suitably qualified and experienced structural engineer. Wind Class Racking Pressure kpa Wind Racking Forces Area of the building fascade facing the wind (m 2 ) Racking Force (kn) N N N3 C N4 C N5 C N6 C Notes This table may be used to determine approximate horizontal wind forces to be resisted by wall bracing and sub-floor bracing. Racking pressures (and the resulting forces) are approximate only, and are calculated in accordance with AS 4055 for gable ends or flat roof buildings. Pitched roofs will result in slightly lower pressures and forces. Separate consideration should be given to horizontal earthquake and/or tsunami loads.

34 Disclaimer & Copyright Disclaimer This training package covers broad engineering principals and building practices, with particular emphasis on affordable housing and associated village infrastructure in the Asia- Pacific region. These broad principals and practices must be translated into specific requirements for particular projects by professional architects, engineers or builders with the requisite qualifications and experience. Associated sample specifications and drawings are available in electronic format, with the express intention that architects, engineers and builders will edit them to suit the particular requirements of specific projects. The design, construction and costing of structures must be carried out by qualified and experienced architects, engineers and builders, who must make themselves aware of any changes to the applicable standards, building regulations and other relevant regulations. The authors, publishers and distributors of these documents, specifications and associated drawings do not accept any responsibility for incorrect, inappropriate or incomplete use of this information. Copyright Quasar Management Services Pty Ltd All rights are reserved. Permission is given for individuals to use this material in the preparation of designs, specification and contracts for individual projects. Permission is also given for not-for-profit Nongovernmental Organizations to use this material in the preparation of Building Skills Training Programs and for the design, specification and construction of affordable housing and associated infrastructure in the Asia-Pacific region. Use of this material for any other commercial purposes prohibited without the written permission of the copyright owner.